U.S. patent application number 10/617515 was filed with the patent office on 2005-01-13 for power supply having multi-vector error amplifier for power factor correction.
Invention is credited to Chen, Chern-Lin, Leu, Yi-Hsin, Lin, Jenn-Yu G., Yang, Ta-yung.
Application Number | 20050007083 10/617515 |
Document ID | / |
Family ID | 33564982 |
Filed Date | 2005-01-13 |
United States Patent
Application |
20050007083 |
Kind Code |
A1 |
Yang, Ta-yung ; et
al. |
January 13, 2005 |
Power supply having multi-vector error amplifier for power factor
correction
Abstract
A regulated power supply having power factor correction control
includes a multi-vector error amplifier. The multi-vector error
amplifier provides an error signal that is used to regulate a
switching mechanism of the power supply. The multi-vector error
amplifier acts to provide a low distortion error signal during
steady-state operation, while responding rapidly and smoothly to
sudden load changes.
Inventors: |
Yang, Ta-yung; (Milpitas,
CA) ; Leu, Yi-Hsin; (IIan City, TW) ; Chen,
Chern-Lin; (Taipei, TW) ; Lin, Jenn-Yu G.;
(Taipei, TW) |
Correspondence
Address: |
J C PATENTS, INC.
4 VENTURE, SUITE 250
IRVINE
CA
92618
US
|
Family ID: |
33564982 |
Appl. No.: |
10/617515 |
Filed: |
July 10, 2003 |
Current U.S.
Class: |
323/282 |
Current CPC
Class: |
H02M 1/4225 20130101;
H02M 1/4275 20210501; Y02B 70/10 20130101 |
Class at
Publication: |
323/282 |
International
Class: |
G05F 001/40 |
Claims
What is claimed is:
1. A regulated power supply having power factor control comprising:
a sample voltage linearly related to an output voltage of said
regulated power supply; and a multi-vector error amplifier for
automatically amplifying said sample voltage at different gains and
bandwidths depending on said sample voltage, comprising: a voltage
adder for adding at least three voltage signals; a steady-state
reference-voltage amplifier, wherein an output of said steady-state
reference-voltage amplifier is connected via a low pass filter to a
first input of said voltage adder; a low reference-voltage
amplifier, wherein an output of said low reference-voltage
amplifier is connected via a first diode to a second input of said
voltage adder; and a high reference-voltage amplifier, wherein an
output of said high reference-voltage amplifier is connected via a
second diode to a third input of said voltage adder.
2. The regulated power supply according to claim 1, wherein said
steady-state reference-voltage amplifier further comprises a
negative input connected to said sample voltage and a positive
input connected to a steady-state reference-voltage.
3. The regulated power supply according to claim 1, wherein said
low reference-voltage amplifier further comprises a negative input
connected to said sample voltage and a positive input connected to
a low reference-voltage, and wherein said low reference-voltage is
distinctly lower than said steady-state reference-voltage supplied
to said steady-state reference-voltage amplifier.
4. The regulated power supply according to claim 1, wherein said
high reference-voltage amplifier further comprises a negative input
connected to said sample voltage and a positive input connected to
a high reference-voltage, and wherein said high reference-voltage
is distinctly higher than said steady-state reference-voltage
supplied to said steady-state reference-voltage amplifier.
5. The regulated power supply according to claim 1, wherein the
bandwidth of said multi-vector error amplifier is significantly
less than the frequency of an input power of the power supply when
said sample voltage is less than said high-reference voltage and
greater than said low-reference voltage.
6. The regulated power supply according to claim 1, wherein the
bandwidth of said multi-vector error amplifier increases
significantly and the gain of said multi-vector error amplifier
decreases significantly when said sample voltage exceeds said
high-reference voltage or decreases below said low-reference
voltage.
7. A regulated power supply having power factor control comprising:
a sample voltage linearly related to an output voltage of said
power supply; and a multi-vector error amplifier for automatically
amplifying said sample voltage at different gains and bandwidths
depending on said sample voltage, comprising: a voltage adder for
adding at least three voltage signals; a current mirror; a first
current source; a steady-state reference-voltage amplifier, wherein
an output of said steady-state reference-voltage amplifier is
connected via a low pass filter and a first diode to a first input
of said voltage adder; a high reference-voltage amplifier, wherein
an output of said high reference-voltage amplifier is connected via
a second diode to a second input of said voltage adder; a low
reference-voltage amplifier, wherein an output of said low
reference-voltage amplifier is connected via a current mirror to a
third input of said voltage adder; and a buffer amplifier, wherein
an input of said buffer amplifier is coupled to said sample
voltage.
8. The regulated power supply according to claim 7, wherein said
steady-state voltage amplifier further comprises a negative input
connected to said sample voltage and a positive input connected to
a steady-state reference-voltage.
9. The regulated power supply according to claim 7, wherein said
low pass filter includes a first resistor and a capacitor.
10. The regulated power supply according to claim 7, wherein said
buffer amplifier further comprises a negative input connected to an
output of said buffer amplifier.
11. The regulated power supply according to claim 7, wherein said
high reference-voltage amplifier further comprises a positive input
connected to a high reference-voltage, and wherein said high
reference-voltage is distinctly higher than the steady-state
reference-voltage supplied to said steady-state reference-voltage
amplifier.
12. The regulated power supply according to claim 7, wherein said
high reference-voltage amplifier further comprises a negative input
connected to an output of said buffer amplifier via a second
resistor, and wherein said negative input is further connected to
said output of said high reference-voltage amplifier via a third
resistor.
13. The regulated power supply according to claim 7, wherein said
low reference-voltage amplifier further comprises a positive input
connected to a low reference-voltage, and wherein the low
reference-voltage is distinctly lower than the steady-state
reference-voltage supplied to said steady-state reference-voltage
amplifier.
14. The regulated power supply according to claim 7, wherein said
low reference-voltage amplifier further comprises a negative input
connected to said output of said buffer amplifier via a fourth
resistor.
15. The regulated power supply according to claim 7, wherein said
voltage adder comprises: a second current source connected to a
current junction; a first input connected to said current junction;
a second input connected to said current junction; a third input
connected to said current junction; and a means for converting a
current into a voltage signal connected to said current junction
and an output of said voltage adder.
16. The regulated power supply according to claim 7, wherein said
means for converting a current into a voltage signal includes a
fifth resistor connected to the ground reference.
17. The regulated power supply according to claim 7, wherein the
bandwidth of said multi-vector error amplifier is significantly
less than the frequency of an input power of the power supply when
said sample voltage is less than said high-reference voltage and
greater than said low-reference voltage.
18. The regulated power supply according to claim 7, wherein the
bandwidth of said multi-vector error amplifier increases
significantly and the gain of said multi-vector error amplifier
decreases significantly when said sample voltage exceeds said
high-reference voltage or decreases below said low-reference
voltage.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention generally relates to the art of power
supplies and more particularly, to a regulated power supply with
power factor correction (PFC) control.
[0003] 2. Description of the Related Art
[0004] Regulated power supplies are used for power conversion in
many applications, including computers, lighting ballasts, and
telecommunications devices. Products consuming 70 watts or more
generally require regulated power supplies with power factor
correction, to reduce power loss and comply with environmental
regulations. In these and other products where significant load
variations are frequent, regulated power supplies capable of
reacting rapidly to sudden load changes are especially
desirable.
[0005] Without power factor correction, an AC/DC power conversion
system will draw current through the rectifier in sharp bursts,
shown in FIG. 1B. These high peak currents cause significant power
losses due to heat dissipation. Furthermore, they can put heavy
stress on the power distribution system and the transmission
lines.
[0006] A power factor correction circuit can almost eliminate these
current ripples by regulating the input current with a feedback
control loop. The power factor correction circuit synchronizes the
rectifier input current with the rectifier voltage output (FIG. 1A)
and the power supply voltage output. The power supply can still
provide the same constant voltage output power with a continuous
and low-peak input current. FIG. 1C demonstrates a power supply's
input current waveform with power factor correction. The lower peak
currents enable the power supply to convert energy very
efficiently, while minimizing the stress on the power distribution
system and the transmission lines.
[0007] To generate a low distortion input current during
steady-state operation, a regulated power supply needs a power
factor correction section with a very low bandwidth error
amplifier. The low bandwidth error amplifier filters out non-DC
components from the power supply output voltage, so that they are
not introduced back into the feedback control loop. Because the
input to the power supply is an AC signal, the output, despite
being a DC signal, will inevitably still contain an AC component.
Within limits, this is acceptable on the output, but for the power
output to remain stable, this component must be removed as much as
possible from the feedback signal. Since the AC component is a low
frequency signal (60-120 Hz), a very low bandwidth error amplifier
is required in the power factor correction circuit to do this.
[0008] Regulated power supplies must also respond quickly to rapid
transients. These can occur whenever the output load changes, the
power supply turns on or off, and when the supply input is affected
by glitches or surges. If the power supply does not react fast
enough in these situations, the output voltage will also change,
possibly beyond the predetermined operating range of the power
supply. This can result in an untimely shut down and possible
circuit damage.
[0009] Unfortunately, achieving low signal distortion and fast
response have traditionally been conflicting goals of regulated
power supply design. A power factor correction circuit with an
error amplifier configured to provide low distortion will react
very slowly to load changes. By the time the output of the power
supply is corrected, either high or low voltage protection alarms
will be reached, and the power supply will shut down. This is
because a typical low bandwidth error amplifier filters out higher
frequency signals from the feedback loop, meaning that it is a
`slow` component. While this is necessary for eliminating current
distortion, it reduces the responsiveness of the power factor
correction circuit.
[0010] Prior-art regulated power supply systems have attempted to
address these conflicting goals by making compromises through the
careful selection of components in the power factor correction
circuit. However, such compromises make it impossible to
simultaneously achieve optimum performance in current distortion
and transient response. For the reasons described above, designing
a power factor correction circuit that simultaneously provides low
signal distortion and rapid transient response is fundamentally
difficult. Low current distortion requires a `slow` error
amplifier, but rapid transient response requires a `fast` error
amplifier.
[0011] The challenge is to design an error amplifier for a power
factor correction circuit that filters out AC component ripple
during steady-state operation, while quickly and smoothly
responding to sudden changes in the output load and the supply
voltage. The ideal would be a flexible circuit that could detect
rapid transients, and temporarily increase its control bandwidth in
response without increasing gain.
[0012] One method of addressing this problem is disclosed in U.S.
Pat. No. 5,619,405. Kammiller et al. discloses a power factor
correction circuit with variable bandwidth control. The invention
comprises of a variable resistance connected to an input of a low
bandwidth amplifier, and control circuitry for switching the
variable resistance in response to output conditions. When the
control circuit senses a change in the output load, the resistance
connected to the input of the low bandwidth amplifier can be
decreased temporarily by a switching mechanism. This allows the
feedback-control circuit to temporarily operate at a higher
bandwidth for improved transient response.
[0013] One drawback of the Kammiller invention is that it fails to
decouple steady-state operation from transient-mode operation.
During steady-state operation, feedback signals pass through a low
bandwidth amplifier. To allow control signals to propagate faster
in response to rapid transients, Kammiller introduces a novel
bandwidth control switching mechanism. This design can increase the
overall speed of the feedback loop, but only to a limited degree.
The output of the bandwidth control mechanism is connected in
series to the input of the low bandwidth amplifier. Transient-mode
feedback control signals are still severely bandwidth-limited by
what is effectively a low-pass filter. The transient response of
the circuit is still subject to limitations imposed by the
requirements of steady-state operation.
[0014] Another drawback of the Kammiller invention is that it is
prone to instability. The resistance switching mechanism claimed by
Kammiller does increase the control bandwidth of the feedback loop
whenever the output voltage exceeds steady-state boundaries.
However, by reducing the resistance attached to the input of the
low bandwidth amplifier at higher circuit frequencies, the
resistance switching mechanism also increases the overall gain of
the feedback circuit. FIG. 2A illustrates the gain characteristic
of the Kammiller invention. It is well known to those skilled in
the art that simultaneously increasing power gain and bandwidth
tends to cause a feedback control system to become unstable. Thus,
oscillations in the output voltage may be observed during on/off
and load change transients. Furthermore, the said resistor
switching mechanism will result in very abrupt and sudden
transitions, further putting stress on the circuit and endangering
stability. FIG. 3A illustrates the transient response of the
Kammiller design.
[0015] Another drawback of the Kammiller invention is that the
transient response is slow. The low bandwidth amplifier introduces
a phase delay into the power factor correction control signal. The
low bandwidth amplifier consists of an amplifier connected to a
capacitance. Despite the resistance switching mechanism, transient
feedback signals must still pass through this component and suffer
a phase delay.
[0016] Another drawback of the Kammiller invention is high
production cost. As explained above, the transient response of the
Kammiller design is susceptible to instability. The maximum output
voltage during transient-mode could be substantially higher than
the steady-state output voltage. To cope with this, it would be
necessary to use a bank capacitance with a high voltage rating on
the output side of the power supply. If the power supply were built
to output 385V-400V DC, it would be necessary to use a bank
capacitance rated at 450V. The increased cost of this is very high
relative to the overall cost of the circuit.
[0017] Finally, the Kammiller invention does not disclose how to
build said resistor switching mechanism that its claims rely upon.
There are no diagrams that show how to construct this component.
Neither there is any detailed explanation or description in any of
the preferred embodiments. Without knowing how to build the
invention, it is difficult to assess. A simple way of designing the
said switching mechanism is not known to the art. Any practical
implementation of the variable resistance mechanism will be
cumbersome and expensive relative to the overall cost of the
circuit. Furthermore, the switching mechanism may introduce other
complications that would need to be addressed. In the absence of a
full disclosure of the method of constructing the said device, it
is necessary to conclude that the Kammiller invention has not
conclusively solved the problems described above.
[0018] It will be apparent to those skilled in the art that both of
the preferred embodiments of the Kammiller invention exhibit the
above stated shortcomings. Thus, a need still remains for a power
factor correction circuit that provides low current distortion with
a fast and stable transient response.
SUMMARY OF THE INVENTION
[0019] It is a general objective of the present invention to
provide a multi-vector error amplifier for the power factor
correction circuit of a regulated power supply, that will reduce
distortion in the power output during steady-state operation, while
correcting transient conditions rapidly and smoothly. This is to be
accomplished by automatically increasing the control bandwidth of
the multi-vector error amplifier, and decreasing the gain, whenever
a load change or other transient condition occurs.
[0020] Another objective of the present invention is to overcome
the disadvantages of prior-art inventions, stated above.
[0021] Another objective of the present invention is to provide a
means of stabilizing current input that is decoupled from the means
of correcting transient conditions, such that both can be optimized
in practice. During steady-state operation, the feedback signal
passes through a low bandwidth amplifier to filter out AC-component
distortion from the control loop. When the control circuitry
detects a significant change in the output voltage, indicating a
load change or other transient condition, the feedback signal can
automatically propagate through a high-bandwidth, low-gain voltage
adder. The requirements of steady-state operation do not affect the
performance of the circuit during transient-mode operation, and
vice-versa.
[0022] Another objective of the present invention is to provide a
multi-vector error amplifier with a rapid transient response.
Transients can include load changes, power on/off, input glitches,
and input surges. The present invention allows high frequency
transient-mode feedback signals to propagate around the low
bandwidth amplifier automatically, without incurring any
significant phase delay.
[0023] Another objective of the present invention is to provide a
multi-vector error amplifier with a soft, smooth transient
response. When a change in operating conditions is detected, the
present invention not only increases the control bandwidth of the
feedback loop, but also simultaneously reduces the gain.
[0024] Another objective of the present invention is to reduce the
production costs of a power factor correction circuit. The present
invention accomplishes the preceding objectives with a simple
design utilizing inexpensive components. Achieving a stable
response to load changes allows the power supply to provide a tight
DC output voltage. This permits the use of a bank capacitance with
a relatively low voltage rating on the output of the power supply.
Furthermore, the present invention can control bandwidth using
little more than a few amplifiers and a voltage adder. It is well
known to those skilled in the art that an inexpensive voltage adder
can easily be built. Still further objects and advantages will
become apparent from a consideration of the ensuing description and
drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0025] The accompanying drawings are included to provide a further
understanding of the invention, and are incorporated in and
constitute a part of this specification. The drawings illustrate
embodiments of the invention and, together with the description,
serve to explain the principles of the invention.
[0026] FIG. 1A is the voltage at the output of the bridge rectifier
of the power supply.
[0027] FIG. 1B is the input current signal of a power conversion
circuit without power factor correction.
[0028] FIG. 1C is the input current signal of a power conversion
circuit with power factor correction.
[0029] FIG. 2A shows the voltage gain characteristic of a prior-art
error amplifier, Kammiller (U.S. Pat. No. 5,619,405).
[0030] FIG. 2B shows the voltage gain characteristic of the
multi-vector error amplifier.
[0031] FIG. 3A shows the transient response of a prior-art error
amplifier, Kammiller (U.S. Pat. No. 5,619,405).
[0032] FIG. 3B shows the transient response of the multi-vector
error amplifier.
[0033] FIG. 4 shows a block diagram of a known regulated power
supply with power factor correction.
[0034] FIG. 5 shows a block diagram of a regulated power supply
with power factor correction using a multi-vector error amplifier
according to the present invention.
[0035] FIG. 6 shows a diagram of another embodiment of the
multi-vector error amplifier used in the power factor correction
circuitry according to the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0036] Referring now to the drawings wherein the contents are for
purposes of illustrating the preferred embodiment of the invention
only and not for purposes of limiting same, FIG. 4 shows a block
diagram of a known regulated power supply with power factor
correction.
[0037] In this circuit, a bridge rectifier 22 receives an AC input
signal 20 at an AC input 24. An output 26 of the bridge rectifier
22 is connected to an inductor 28 and a current-sense resistor 30.
The inductor 28 and the current-sense resistor 30 are connected
together to form a loop, through a switch 32. The switch 32 may be
any of several components, including a FET switch or some other
type of known switching device.
[0038] When the control circuitry closes the switch 32, the voltage
from the bridge rectifier 22 is applied to the inductor 28. The
current passing through the inductor 28 starts to increase.
Eventually, the switch 32 opens and the current flowing through the
inductor 28 flows through a diode 36 to charge a capacitor 42. The
capacitor 42 is discharged when necessary by a load across a
terminal pair 34. While it is conductive, the diode 36 keeps the
capacitor 42 from discharging through the switch 32. The control
signal for the switch 32 operates to maintain a nearly constant
voltage at terminals 34. It is to be appreciated that while the
output in this embodiment is 385 volts, other constant voltage
outputs are possible.
[0039] The switch 32 is controlled by a drive circuit 44, which in
turn receives its input from a control device such a RS latch. A
set-input and a reset-input of a RS latch 46 are shown in this
embodiment to be respectively coupled from a comparator 48 and a
clock 50. The clock 50 generates a clock signal operating at
approximately 100 KHz. The operation of these elements is known in
the art and, therefore, does not need to be discussed in greater
detail.
[0040] In this prior art embodiment a sample of the output voltage
is sensed at a voltage divider location 39. The voltage divider
location 39 is part of a high impedance divider network formed by a
resistor 38 and a resistor 40. The voltage divider location 39 is
connected to an input of a low bandwidth error amplifier block 100.
The steady-state sensed output voltage of the voltage divider
location 39 can be configured to be any value, but in this
embodiment it is chosen to be 2.5 Volts.
[0041] The input of the low bandwidth error amplifier block 100 is
connected to a buffer amplifier 101, to avoid loading the high
impedance divider network. The output of the buffer amplifier 101
is provided to a negative input of an amplifier 110 via a resistor
111. A capacitive element 112 is connected from the negative input
to an output of amplifier 110. The capacitive element 112 increases
the impedance and reduces the bandwidth of the low bandwidth error
amplifier block 100. It is to be appreciated that the error
amplifier 110 may also be called an integrator, comparator, voltage
comparator, voltage error amplifier, limited bandwidth amplifier,
or other terms known in the art.
[0042] The sampled signal from the buffer amplifier 101 is compared
in error amplifier 110 with a reference voltage V.sub.REF of 2.5
Volts. This comparison operation produces a voltage error signal
60, which is supplied to a multiplier/divider block 62. The
multiplier/divider block 62 also receives, through a resistor 64, a
line shape current 66 having the same shape as a rectified input
voltage of the power supply. Also provided to the
multiplier/divider block 62 is a magnitude input 68. The magnitude
input 68 is a DC signal that is related to a RMS value of a supply
line voltage, which can vary. The magnitude input signal 68 is
created by passing a rectified line signal 70 first through a low
pass filter 72 and then through a squarer 74, to obtain a DC signal
related to the square of the supply line voltage.
[0043] The three inputs, the voltage error signal 60, the line
shape current 66, and the magnitude input 68 are combined within
multiplier/divider block 62 and converted to a current by a
resistor 78. This forms an input current 76, which is the reference
signal for the comparator 48, and which is applied to a negative
input of comparator 48 via the resistor 78. The input current 76 is
compared with a line input current 79. The line input current 79
creates a voltage across a resistor 30, which is converted to a
current by a resistor 80 and applied to the negative input of the
comparator 48. A positive input of the comparator 48 is tied to a
ground point of the terminal pair 34. The control loop formed by
the terminal pair 34, the resistor 38, the voltage divider location
39, the resistor 40, the low bandwidth error amplifier block 100,
the voltage error signal 60, the multiplier/divider block 62, the
resistor 64, the line shape current 66, the magnitude input 68, the
rectified line signal 70, the low pass filter 72, the squarer 74,
the input current 76, the resistor 78, the current 79, the resistor
80, the current-sense resistor 30, and the comparator 48, maintains
a voltage at the junction of resistors 78 and the resistor 80, at
the level of the ground point of the terminal pair 34.
[0044] As previously noted, an output of the comparator 48, clock
50, the RS latch 46, and the drive circuit 44 operates to provide a
desired output voltage across the terminal pair 34, by controlling
switch 32.
[0045] The power supply illustrated in FIG. 4 is designed to
maintain a constant DC output voltage, such as 385 volts. The
distortion in the output voltage signal must remain within
acceptable limits, such as +10/-10 Volts. However, the terminal
pair 34 is connected across the capacitive element 42, which is
charged by a rectified current having a large 120 Hz component, so
the voltage sensed at the voltage divider location 39 will still
have a 120 Hz AC ripple component. If this AC component is included
as part of the voltage error signal 60 and passed on to the
multiplier/divider block 62, then the input current 76 will contain
the undesirable distortion component from the waveform across the
capacitive element 42. To avoid this, the voltage error signal 60
needs to be as close as possible to the pure DC component of the
output signal. To accomplish this, the low bandwidth error
amplifier block 100 must operate at a very low bandwidth to filter
out AC signal components. However, this also results in a very slow
response to load changes.
[0046] The DC voltage error signal 60 will be a constant DC voltage
signal with different values, depending on load and input
conditions. The very low bandwidth amplifier block 100 will filter
out the AC component of the sampled voltage from the voltage
divider location 39. This enables providing a voltage error signal
60 to multiplier/divider block 62, almost completely free of AC
distortion. It is to be noted that no distortion is input by the
line shape current 66 or the magnitude input 68.
[0047] A problem with the regulated power supply of FIG. 4 is that
when a large fast load change occurs at the terminal pair 34, the
low bandwidth error amplifier block 100 is too slow to follow the
change. When a sudden load step occurs, it is desirable for the
power supply to respond quickly by increasing or decreasing the
output current, without allowing the output voltage level to
change. One means for the low bandwidth error amplifier block 100
of achieving this, would be by increasing the speed of the
response, by increasing bandwidth and correcting the voltage output
level before it can change significantly. It is further desirable
for this reaction to occur smoothly. While increasing bandwidth,
the circuit should also reduce gain, in order to achieve a rapid
and stable transient response. It should be further noted that the
regulated power supply of FIG. 4 faces a similar problem when the
input delivered to the power supply suddenly changes. This can
happen either because the power supply is turned on/off, or because
the input voltage experiences a glitch.
[0048] Therefore, with respect to a power supply with power factor
correction, capable of providing an output signal with low
distortion, and a rapid yet stable response to load and input
changes, attention is directed to FIG. 5. Components similar or
identical to those in FIG. 4 are assigned the same numbers. The
present invention specifically relates to a multi-vector error
amplifier block 200. This component replaces the low bandwidth
error amplifier block 100 from FIG. 4, with the purpose of ensuring
that the drive signal of the switch 32 will operate to provide a
low distortion output, with a quick and stable response to load and
input changes. An input of the multi-vector error amplifier block
200 is connected to the voltage divider location 39, and an output
of the multi-vector error amplifier block 200 outputs the voltage
error signal 60.
[0049] During steady-state operation, the circuit operates in a
manner similar to that of the low bandwidth error amplifier 100
described above, so that the power factor control circuitry of the
regulated power supply provides a low distortion output voltage.
However, with respect to the multi-vector error amplifier block
200, additional elements are provided, so that the power supply
responds quickly and smoothly to fast large load changes, and input
transients. When the power supply is operating within acceptable
steady-state parameters, the multi-vector error amplifier block 200
has a low bandwidth, thereby operating appropriately in a slow
manner. When a large fast transient change occurs at the load or at
the input, the output voltage will begin changing. At this point,
operation of the multi-vector error amplifier block 200 will change
automatically to a high bandwidth, low gain mode, to correct the
change in the output voltage as soon as possible.
[0050] As long as operating conditions remain steady, the voltage
divider location 39 will be very close to the reference voltage 2.5
Volts in this embodiment. This voltage divider location 39 is
connected to an input of the multi-vector error amplifier block
200. As long as this voltage level remains stable, the multi-vector
error amplifier will be equivalent to the low bandwidth error
amplifier 100 of FIG. 4 in terms of its operation.
[0051] During steady-state operation the feedback signal will only
be able to pass through an amplifier 210. A negative input of the
amplifier 210 is connected to an input of the multi-error vector
amplifier block 200, and a positive input of the amplifier is
connected to a steady-state reference voltage of 2.5 Volts. An
output of the amplifier 210 is connected to a voltage adder 300 via
a resistor 211 and a shunt capacitor 212. An output of the voltage
adder 300 is connected to the output of the multi-vector error
amplifier block 200.
[0052] In this embodiment, to make error amplifier 210 slow
changing, the resistor 211 and the shunt capacitor 212 can easily
be made large enough, so that the combination of these components
will have a bandwidth much lower than the AC frequency, such as 60
Hz. By configuring the multi-vector error amplifier block 200 in
this manner, virtually zero AC ripple is allowed to pass through
the multi-vector error amplifier. During steady-state operation,
the output of the voltage adder 300 will only consist of this low
bandwidth component from the feedback. The output of the voltage
adder 300 becomes the voltage error signal 60, which will be
sufficiently free of non-DC components to enable the power supply
to produce a low interference output signal.
[0053] As previously discussed, however, it is common for power
supplies to experience sudden load changes, and abrupt input
transients. During these periods the low bandwidth error amplifier
block 100 of FIG. 4 will not be able to maintain a constant voltage
output, and therefore the regulated power supply will be in danger
of entering a non-regulated state. The present invention speeds up
the operation of the power factor correction subsection while
improving stability, by adding extra components designed to handle
transient conditions effectively.
[0054] The input of the multi-vector error amplifier block 200 is
also connected to a negative input of an amplifier 220, used to
detect sudden increases in the output voltage. A high reference
voltage of 2.6 Volts is connected to a positive input of the
amplifier 220. An output of the amplifier 220 is connected to a
cathode of a diode 221. An anode of the diode 221 is connected to a
second input of the voltage adder 300. When the sampled voltage at
the divider location 39 exceeds the high reference voltage, the
amplifier 220 will allow a high-bandwidth signal to pass through
the diode 221 to the voltage adder 300, in the form of a negative
current. The gain of this signal can be controlled through the
selection of an appropriate amplifier component 220.
[0055] The input of multi-vector error amplifier block 200 is also
connected to a negative input of an amplifier 230, used to detect
sudden decreases in the output voltage. A low reference voltage of
2.4 Volts is connected to a positive input of the amplifier 230. An
output of the amplifier 230 is connected to an anode of a diode
231. A cathode of the diode 231 is connected to a third input of
the voltage adder 300. When the voltage at the divider location 39
dips below the low reference voltage, it will indicate that the
output voltage is beginning to decrease. When the sampled voltage
at the divider location 39 exceeds the low reference-voltage, the
amplifier 230 will allow a high-bandwidth signal to pass through
the diode 231 to the voltage adder 300. The gain of this signal can
be controlled through the selection of an appropriate amplifier
component 230.
[0056] These components are arranged so that when sudden changes in
output/input conditions are detected, the feedback signal can
propagate through a high bandwidth, low gain path, instead of the
low bandwidth amplifier 210 section. When the power supply is in
steady-state operation, these added components do not affect the
remainder of the circuit, and it operates to reduce signal
distortion, in a fashion similar to that of the prior art in FIG.
4.
[0057] It is to be understood that this constitutes an explanation
of one possible method of constructing the multi-vector error
amplifier block 200 according to the present invention. For another
explanation of how to construct the multi-vector error amplifier
block 200 according to the present invention, attention is turned
to FIG. 6. This diagram shows another implementation of the
multi-vector error amplifier block 200. Specifically, it includes
some auxiliary components omitted from FIG. 5, and it demonstrates
how to build the voltage adder 300.
[0058] The sampled voltage at the voltage divider location 39 is
connected to an input of the multi-vector error amplifier block
200. A negative input of an amplifier 210 is connected to this
input. A positive input of the amplifier 210 is connected to a
steady-state reference voltage of 2.5 Volts. To keep the bandwidth
of the multi-vector error amplifier block 200 low during
steady-state operation, an output of the amplifier 210 is connected
to a low pass filter consisting of a series resistor 211 and a
shunt capacitor 212. The output of the low pass filter is connected
to a cathode of a diode 213. The anode of the diode 213 is
connected to a first input of the voltage adder 300. These
components act to regulate the operation of the power supply during
steady-state operation, in a manner similar to that of the
embodiment described above.
[0059] The multi-vector error amplifier block 200 further includes
an amplifier 220 and an amplifier 230, to enable a quick and stable
response to sudden changes input/output changes. To avoid loading
the high impedance divider network formed by resistors 38 and 40,
the voltage divider location 39 is not connected directly to the
amplifiers 220 and 230. Instead, the voltage divider location 39 is
first connected to a positive input of a buffer amplifier 201. An
output of the buffer amplifier 201 is connected back to a negative
input of the buffer amplifier 201.
[0060] An amplifier 220 is a high reference-voltage amplifier. It
is included so that the multi-vector error amplifier block 200 can
react rapidly when the output voltage begins to increase. The
output of the buffer amplifier 201 is connected to a negative input
of the amplifier 220 via a resistor 222. In this embodiment, a
positive input of the amplifier 220 is connected to a high
reference voltage of 2.6 Volts. An output of the high
reference-voltage amplifier 220 is connected to the negative input
of the amplifier 220 via a resistor 223. The output of the high
reference-voltage amplifier 220 is connected to a cathode of a
diode 221. The anode of the diode 221 is connected to a second
input of the voltage adder 300.
[0061] When the voltage at the voltage divider location 39 exceeds
2.6V, this indicates the output voltage of the power supply is
increasing suddenly. The amplifier 220 will allow a high-bandwidth
signal to pass through the diode 221 to the voltage adder 300, in
the form of a negative current. This current will cause an output
voltage of the voltage adder 300 to rapidly decrease, quickly
reducing the switching frequency and the output voltage of the
power supply. Adjusting the ratio of the resistor 222 and the
resistor 223 can reduce the gain of this high-bandwidth signal.
[0062] An amplifier 230 is a low reference-voltage amplifier. It is
included so that the multi-vector error amplifier block 200 can
react appropriately when the output voltage begins to decrease
suddenly. The output of the buffer amplifier 201 is connected to a
negative input of the amplifier 230 through a resistor 232. In this
embodiment, a positive input of the amplifier 230 is connected to a
low reference voltage signal of 2.4 volts. An output of the low
reference-voltage amplifier 230 is connected to a third input of
the voltage adder 300 via a current mirror.
[0063] The current mirror mentioned above consists of a MOSFET 237
and a MOSFET 238. The output of the low reference-voltage amplifier
230 is connected to a gate of a MOSFET 236. The negative input of
the amplifier 230 is connected to a source of the MOSFET 236. A
drain of the MOSFET 236 is connected to a drain of the MOSFET 237,
a gate of the MOSFET 237, and a gate of the MOSFET 238. A source of
the MOSFET 237 and a source of the MOSFET 238 are tied together,
and connected to the current source 235. A drain of the MOSFET 238
connects to the third input of the voltage adder 300. The operation
of current mirrors is known in the art and, therefore, does not
need to be discussed in greater detail.
[0064] When the voltage at the voltage divider location 39 goes
below 2.4V, this indicates the output voltage of the power supply
is decreasing suddenly. The amplifier 230 will allow a
high-bandwidth signal to pass through the current mirror to the
voltage adder 300. This current will cause the output voltage of
the voltage adder 300 to quickly increase, rapidly increasing the
switching frequency of the power supply, and quickly increasing the
output voltage of the power supply. Increasing the resistor 232 can
reduce the gain of this high-bandwidth signal.
[0065] The voltage adder 300 includes three inputs, a current
source 301, a current junction point 310 and a shunt resistor 320.
The current source 301 acts as a bias for the voltage adder 300.
The voltage adder 300 sums up the currents of the three inputs at
the current junction point 310. The current junction 310 is
connected to the output of the multi-vector error amplifier block
200. The shunt resistor 320 connected to the multi-vector error
amplifier block 200 turns the output of the current junction point
310 into a voltage signal. This output of the voltage adder 300
becomes the output of the multi-vector error amplifier block 200
and the voltage error signal 60.
[0066] It will be apparent to those skilled in the art that various
modifications and variations can be made to the structure of the
present invention without departing from the scope or spirit of the
invention. In view of the foregoing, it is intended that the
present invention cover modifications and variations of this
invention provided they fall within the scope of the following
claims or their equivalents.
* * * * *